Embryology of Branchial Arches (Applied Anatomy)

1. Embryology of Branchial
Arches & Nerve Supply
((Applied Anatomy
By: Osama Elhamzawy
Faculty of Medicine
Alexandria University - Egypt

2. Introduction:
During the pre –Embryonic period, the cells
differentiate into three germ layers:
Ectoderm (outside layer(
Mesoderm (middle layer(
Endoderm (inside layer(

3. Introduction:
 Ectoderm gives rise to the CNS, peripheral nervous
system; sensory epithelia of the eye, ear, and nose;
epidermis and its appendages (hair and nails(.
 Neural crest cells derived from neuroectoderm, give rise
to the cells of the spinal, cranial (cranial nerves V, VII, IX,
and X(, and autonomic ganglia; ensheathing cells of the
peripheral nervous system; pigment cells of the dermis;
muscle, connective tissues, and bone of pharyngeal arch
origin and meninges (coverings( of the brain and spinal
cord.

4. Introduction:
 Mesoderm gives rise to connective tissue; cartilage; bone;
striated and smooth muscles; blood, and lymphatic
vessels; heart, kidneys; ovaries; testes; genital ducts;
serous membranes lining the body cavities (pericardial,
pleural, and peritoneal(; spleen; and cortex of suprarenal
glands.
 Endoderm gives rise to the epithelial lining of the
gastrointestinal and respiratory tracts, urinary bladder ,
tympanic cavity, tympanic antrum, and auditory tube
parenchyma of the tonsils, thyroid and parathyroid glands,
thymus, liver, and pancreas.

5. Pharyngeal
arches begin to develop
Arches
 The pharyngeal
early in the
fourth week as neural crest cells migrate into the
future head and neck regions.
 The first pair of pharyngeal arches, the primordium of
the jaws, appears as surface elevations lateral to the
developing pharynx.
 Soon other arches appear as obliquely disposed,
rounded ridges on each side of the future head and
neck regions.

7. Pharyngeal
Arches
fourth week, four
 By the end of the
arches are visible externally.
pairs of pharyngeal
 The fifth and sixth arches are rudimentary and are not
visible on the surface of the embryo.
 The pharyngeal arches are separated from each other by
the pharyngeal grooves. Like the pharyngeal arches, the
grooves are numbered in a craniocaudal sequence.

9. Pharyngeal Apparatus
Pharyngeal apparatus consists of:
 Pharyngeal arches
 Pharyngeal pouches
 Pharyngeal grooves
 Pharyngeal membrane

11. Pharyngeal Arch Components

Each pharyngeal arch consists of a core of
mesenchyme

Is covered externally by ectoderm and internally
by endoderm

In the third week the original mesenchyme is
derived from mesoderm

But during the fourth week most of the
mesenchyme is derived from neural crest cells
that migrate into the pharyngeal arches

12. Fate of Pharyngeal Arches

During the fifth week, the second pharyngeal
arch enlarges and overgrows the third and fourth
arches, forming the ectodermal depression
called cervical sinus

By the end of seventh week the second to fourth
pharyngeal grooves and the cervical sinus have
disappeared, giving the neck a smooth contour

14. Fate of Pharyngeal Arches
A typical pharyngeal arch contains:

An aortic arch, an artery that arises from the truncus
arteriosus of the primordial heart

A cartilaginous rod that forms the skeleton of the arch

A muscular component that differentiates into muscles
in the head and neck

A nerve that supplies the mucosa and muscles derived
from the arch

16. First Pharyngeal Arch cartilage

The dorsal end (Meckel cartilage) ossifies to
form malleus and incus

The middle part forms anterior ligament of
malleus (sphenomandibular ligament)

Ventral part forms primordium of the mandible

The cartilage disappears as mandible develops
around it

18. Second Pharyngeal Arch
cartilage

The dorsal end (Reichert cartilage) ossifies to
form the stapes and styloid process of the
temporal bone

The ventral end ossifies to form the lesser cornu
and superior part of the body of the hyoid bone

Its perichondrium forms the stylohyoid ligament

19. Third, Fourth, Fifth and Sixth
Pharyngeal Arches cartilages

The third arch cartilage ossifies to form the
greater cornu and the inferior part of the body of
the hyoid bone

The fourth and sixth arch cartilages fuse to form
the laryngeal cartilages except epiglottis which
develops from hypopharyngeal eminence

The fifth pharyngeal arch is rudimentary and has
no derivatives

20. Derivatives of Pharyngeal Arch
Muscles

The musculature of the first pharyngeal arch forms the
muscles of mastication

The second pharyngeal arch forms the stapedius,
stylohyoid, posterior belly of digastric, auricular and
muscles of facial expression

The third arch forms the stylopharyngeus

The fourth arch forms cricothyroid and constrictors of
pharynx

Sixth pharyngeal arch forms the intrinsic muscles of the
larynx

22. Derivatives of Pharyngeal Arch
Nerves






The first pharyngeal arch supplied by the caudal two
branches of Trigeminal nerve (maxillary and mandibular)
The second pharyngeal arch supplied by facial nerves
supply, and caudal (fourth to sixth) arches respectively
The third pharyngeal arch supplied by glossopharyngeal
nerve
Fourth to sixth supplied by vagus
The fourth arch is supplied by superior laryngeal branch
of vagus nerve
The sixth arch is supplied by its recurrent laryngeal
branch

24. Pharyngeal Pouches

There are four well defined pairs of pharyngeal
pouches

The pairs of pouches develop in a craniocaudal
sequence between the arches

The fifth pair is absent or rudimentary

25. Pharyngeal Pouches
 The endoderm
of the pouches contacts
the ectoderm of the pharyngeal grooves
and together they form the double layered
pharyngeal membranes that separate the
pharyngeal pouches from the pharyngeal
grooves

27. First Pharyngeal Pouch

The first pharyngeal pouch expands into an
elongate tubotympanic recess

And forms the endoderm lines the future
Eustachian tube , middle ear, mastoid antrum.

And inner layer of the tympanic membrane

28. Second Pharyngeal Pouch

The second pharyngeal pouch is largely
obliterated as the palatine tonsils develop

Part of the cavity of this pouch remains as the
tonsillar sinus or fossa

The endoderm of the pouch proliferates and
grows into the underlying mesenchyme

The central parts of these buds form crypts

30. Second Pharyngeal Pouch
 The
pouch endoderm forms the surface
epithelium and the lining of the tonsillar
crypts
 At
about 20 weeks the mesenchyme
around the crypts differentiates into
lymphoid tissue
 These
tissues soon organizes into the
lymphatic nodules of the palatine tonsil

31. Third Pharyngeal Pouch

The third pharyngeal pouch expands and
develops a solid, dorsal bulbar part and a
hollow elongate ventral part

Its connection with the pharynx is reduced to a
narrow duct that soon degenerates

By the sixth week the epithelium of each dorsal
bulbar part begins to differentiate into inferior
parathyroid gland

32. Third Pharyngeal Pouch

The epithelium of the elongate ventral parts of third
pharyngeal pouch (primordia of thymus) proliferates and
their cavities obliterate

These bilateral primordia of thymus come together in the
median plane to form thymus

It descends into the superior mediastenum

The bilobed form of thymus remains throughout life

Each lobe has its capsule own blood supply, lymphatic
drainage and nerve supply

34. Third Pharyngeal Pouch
 The
primordia of thymus and parathyroid
glands lose their connections with the
pharynx and migrate into the neck
 Later
the parathyroid glands separate
from the thymus and lie on the dorsal
surface of the thyroid gland

35. Fourth Pharyngeal Pouch

The fourth pharyngeal pouch also expands into
dorsal bulbar and elongate ventral parts

Its connection with the pharynx is reduced to a
narrow duct that soon degenerates

By the sixth week, each dorsal part develops
into a superior parathyroid gland

It lies on the dorsal surface of the thyroid gland

36. Fourth Pharyngeal Pouch
 The
parathyroid glands derived from the
third pouches descend with the thymus
and are carried to a more inferior position
than the parathyroid derived from the
fourth pouches
 This
explains why the parathyroid glands
derived from the third pair of pouches are
located inferior to those from the fourth
pouches

37. The Fifth Pharyngeal Pouch
 When
this develops, this rudimentary
pouch becomes part of the fourth
pharyngeal pouch and helps to form the
ultimopharyngeal body that gives the
calcitonin producing cells (parafollicular
cells or C cells of the thyroid gland)

38. Pharyngeal Grooves

Only first pair persists as the external acoustic
meatus

The other grooves normally obliterated with the
cervical sinus as the neck develops

39. Pharyngeal Membranes

These membranes form where the epithelia of
the grooves and pouches approach each other

Only first pharyngeal membrane becomes the
tympanic membrane, others obliterate

40. Birth Defects
Involving the
Pharyngeal Region

41. Birth Defects Involving the Pharyngeal Region
1. Ectopic Thymic and Parathyroid Tissue
2. Branchial Fistulas
3. Neural Crest Cells and Craniofacial Defects
• Treacher Collins syndrome (mandibulofacial
dysostosis)
• Robin sequence
• DiGeorge anomaly
• Velocardiofacial syndrome (VCFS) and conotruncal
anomalies face syndrome
• Oculoauriculovertebral spectrum (Goldenhar
syndrome)
4. Thyroglossal Duct and Thyroid Abnormalities
5. Face anomalies
6. Palate anomalies

42. Birth Defects Involving the Pharyngeal Region
1. Ectopic Thymic and Parathyroid Tissue:
Since glandular tissue derived from the pouches
undergoes migration ; accessory glands or remnants of
tissue may persist along the pathway particularly for
thymic tissue, which may remain in the neck, and for
the parathyroid glands.
The inferior parathyroids are more variable in position than
the superior ones and are sometimes found at the
bifurcation of the common carotid artery.

43. Birth Defects Involving the Pharyngeal Region
2. Branchial Fistulas
•
•
•
•
When the second pharyngeal arch fails to grow caudally over the third
and fourth arches, leaving remnants of the second, third, and fourth
clefts in contact with the surface by a narrow canal.
These cysts are always on the lateral side of the neck in front of the
sternocleidomastoid muscle.
They commonly lie under the angle of the mandible and do not enlarge
until later in life.
Internal branchial fistulas are rare and occur when the cervical sinus is
connected to the lumen of the pharynx by a small canal, which usually
opens in the tonsillar region.

46. Birth Defects Involving the Pharyngeal Region
3. Neural Crest Cells and Craniofacial Defects
Crest cells also contribute to the conotruncal
endocardial cushions which septate the outflow
tract of the heart into pulmonary and aortic channels
So many infants with craniofacial defects may also
have cardiac abnormalities such as:
•Persistent truncus arteriosus
•Tetralogy of Fallot
•Transposition of the great vessels

47. Birth Defects Involving the Pharyngeal Region
Examples of craniofacial defects involving crest cells:
1. Treacher Collins syndrome
(mandibulofacial dysostosis)
inherited as an autosomal dominant trait
60% of cases arising as new mutations
Characterizaed by :
•Malar hypoplasia due to underdevelopment of
the zygomatic bones
•Mandibular hypoplasia
•Down-slanting palpebral fissures
•Lower eyelid colobomas
•Malformed external ears

48. Birth Defects Involving the Pharyngeal Region
2. DiGeorge anomaly:
Characterizaed by:
•Microstomia
•Partial or complete absence of the thymus
•immunological deficiencies
•Hypocalcemia
Prognosis:
Poor

49. Birth Defects Involving the Pharyngeal Region
3. Oculoauriculovertebral spectrum
(Goldenhar syndrome)
Characterized by:
•Number of craniofacial abnormalities that
usually involve the maxillary, temporal, and
zygomatic bones, which are small and flat.
•Ear (anotia, microtia)
•Eye (tumors and dermoids in the eyeball)
•Vertebral (fused hemivertebrae
spina
bifida)
•Cardiac abnormalities (Tetralogy of Fallot
and ventricular septal defects)

50. Birth Defects Involving the Pharyngeal Region
4. Thyroglossal Duct and Thyroid
Abnormalities
lie at any point along the
migratory pathway of the
thyroid gland but is always
near or in the midline of the
neck
Thyroglossal fistula
Usually arises secondarily after
rupture of a cyst but may be
present at birth.

52. Birth Defects Involving the Pharyngeal Region
5- Face anomalies

53. Birth Defects Involving the Pharyngeal Region
5- Face anomalies

54. Birth Defects Involving the Pharyngeal Region
5- Face anomalies
1-cleft upper lip:
•May be uni/bilateral
•There is a defect between the philtrum and the lateral part of the lip
•It is due to failure of fusion between the maxillary process and intermaxillary
process
•Common in males
2-oblique facial cleft:
•It is a defect in the face from the medial angle of the eye crossing the side of the
nose to the upper lip
•It is due to failure of fusion between Maxillary process and the lateral and medial
nasal processes
•Nasolacrimal duct is exposed to ant.
3-median cleft lower lip:
•It is due to failure of fusion between the mandibular processes (rare)

55. Birth Defects Involving the Pharyngeal Region
5- Face anomalies
4-macrostomia:
It is due to arrest of fusion between Maxillary and mandibular processes to shift
the angles medially
5-microstomia:
It is due to excessive fusion bet. The maxillary and mandibular processes

56. Birth Defects Involving the Pharyngeal Region
5- Face anomalies

57. Birth Defects Involving the Pharyngeal Region
5- Face anomalies

58. Birth Defects Involving the Pharyngeal Region
6- Palate anomalies
1-cleft palate:
Fomes:
•Bifid uvula
•Cleft soft palate
•Cleft hard palate and soft palate
It is due to failure of fusion between the two palatine processes posterior or with the
primary palate anterior
2-perforated palate:
•It is due to failure of fusion between The 2 palatine processes at certain point at
midline.

59. Birth Defects Involving the Pharyngeal Region
6- Palate anomalies